Birds of prey circle above the fields. Elegant and powerful, ready to make a deadly move at any moment. McAllen is a paradise for ornithologists. Especially in early spring. On hot summer days, temperatures can soar to over 40 degrees Celsius in the shade.

"No one is outside then," says Jose Cruz, who was born here. He knows almost every twist and turn in the Rio Grande, a natural border between Mexico and the US state of Texas - worlds apart. The border between the US and Mexico is 3,145 km (1,954 miles) long in total.

Illegal migration is one of the main themes of this year's election campaigns. Republican presidential front-runner Donald Trump wants to build a wall to stop illegal immigration from Mexico, a subject that crops up in every political debate that he takes part in.

Jose Cruz has spent many years living and working abroad, controlling borders for the UN and organizing border controls in Kosovo and Macedonia. Now he is back at home, protecting his people.

"The United States is founded by immigrants. I am not against immigration," he insists. "But we have to find ways to control who enters our country." His eyes are intense and dark. What color eyes do eagles have?

Understaffed and archaic technology

"The official border control isn't able to offer this protection," because there is neither enough staff nor adequate, up-to-date equipment, he says. He has been working for a private organization - the International Security Agency (ISA) - in McAllen for three years now. "We monitor the areas that we are responsible for with photo and infrared technology. The system is fully automatic and sends signals when something happens." The instruments they use follow the movement. "You have to know where they are. You don't have to guess."

Currently, the company is mainly commissioned by farmers in the border region seeking protection from drug cartels and human smugglers, who apparently use more than verbal threats when they are prevented from conducting their trafficking.

Cruz and his colleagues would prefer to work for the state. "We get a lot of support for our ideas, but no money." He says that politicians are less willing to invest in useful technology than invisible preventative measures "like this huge wall."

Even if he is basically a supporter of Trump, he does not have much respect for this idea. "Everything which slows down illegals is good. But it doesn't stop them. We need a digital fence. We need ground alert all over."

Cruz is not worried about migrants from Mexico and other Latin American states. "They get checked and if they are fleeing violence or war it's fine for them to stay." He is more worried that radical Islamists will enter the US via the poorly secured border. "These are the really dangerous people. And they never would be stopped by a fence. It's so easy to bring a ladder or something."

No Man's Land

An iron fence has been built over the previous decades at massive cost. Rusting structures, between two and six meters high, tower into the sky. There are security cameras, but Cruz says they make no sense and should be placed in the 20-mile wide no man's land between Mexico and the US, which is often a dead zone for migrants in summer. "You have to detect them earlier, once they've made it to the fence, it's too late."

The deep blue sky is reflected in the Rio Grande. A fisherman wades through a shallow spot. Real Hollywood. Suddenly he stops, drops his fishing rod and rushes to the riverbank. To the other side. The Mexican side. Jose Cruz races back to his vehicle, a black GMC Denali. He looks at one of his phones. A bit later, he reads a local TV station's online report. There was a shooting nearby. Nobody was injured. It is not uncommon for shots to be fired from the Mexican border. "These are not regular immigrants. These are the cartels. They try to scare the border controls and clear the space for their operations."

"The river is alive," says Cruz, explaining that it changes course after every flood. That's why it is so difficult to monitor using conventional means.

A violent father

Diego Manche was seven when his mother sent him and his little sister to swimming lessons. The situation at home was becoming more and more unbearable. Their father would start drinking on Thursday and would not stop until Sunday night. The home was his paternal grandparents' house in Mexico City.

"It was always loud, and my parents were fighting a lot, but I remember that the tension changed," he explains. His father started hitting his mother, then him and his sister. "And the rest of my father's family didn't help. I don't talk to them very often," he says today, 15 years later.

He did not understand at the time that his mother was trying to get a visitor's visa for the US. "I just felt that she was really upset at some point and really disappointed." But she never gave up because that was not her style. "She kept the family going from day one."

One day in June 2002, Diego's mother suddenly turned up at school with two suitcases. Diego got on a plane for the first time in his life. They flew to Monterrey, and then they took a bus to Piedras Negras, some 400 km (248 miles) north of McAllen. It was a long time till he flew again.

His maternal grandmother and his aunt had already been in the US for some time. They had a visa which allowed them to cross the border. "We met them. I didn't understand why my mother gave them our two suitcases. Just keeping one extra set of dry clothes for each of us. I still remember this last long hug from my grandmother."

Dry clothes in a plastic bag

They hid in an abandoned house in the border zone with two other women and several children. It was Saturday. Diego's mother argued with strangers. Years later, she explained that that she had paid for false papers, but nobody was willing to believe her. A stranger turned up, instructed them to change as soon as they got to the other side of the river and leave behind their wet clothes. Everything went really fast from then on. He pushed Diego, his sister and their mother into the water. They clung desperately to a black tire while the man swam ahead. Diego does not know how long they spent in the water. The man threw plastic bags of dry clothes on the other bank, waited till they had clambered to land and disappeared.

"I didn't pay attention to where he went. I was amazed by the sight of white people playing soccer within yards of the border as if it didn't exist." He has not forgotten all the wet clothes. "I wished I had my phone then to take a picture. It was so strange."

Suddenly, the children were on the backseat of a car, lying so that no one could see them. There was a female driver, and their mother sat in front.

They made it to San Antonio, where they had a family, without being asked for their papers. "My mom is very religious. She prayed the whole time to Maria de Guadalupe. Maybe it was pure luck. Maybe she helped," says the otherwise cheerful 22-year-old solemnly.

Brutal camp conditions

Migrants who get caught are taken to camps. Kimberly Rivera tried to escape to the US from Honduras via Mexico with her two children. She is in tears as she describes the inhumane conditions in the camp, the lack of food, the brutality of the wardens. "We were thirsty and didn't get enough to drink. They took everything. Also my personal belongings. My kids saw other people in the camp who committed suicide." After registration, a long wait began. It can take years before a decision is made. The 27-year-old is scared that she will have to go back, that she will be tortured or even murdered like so many of her friends and relatives.

For his part, Diego grew up in a relatively wealthy suburb of San Antonio populated mainly by whites, where his aunt has a successful cleaning business.

He started going to a bilingual school. He was a fast learner and picked up English immediately. "Sometimes I wished I had a little accent, that would show where I'm from." He was small and wiry, soon picking up the differences between Mexican football and American football. He was a good runner. Running is not as dangerous as other sports. His mother insisted that he look after himself since the family did not have health insurance.

Keeping mum

It was years before he really understood that something fundamental separated him from his classmates. To begin with, he thought he could not go on school excursions because of money. His mother made him swear on Santa Maria de Guadalupe that he would never tell anybody that they were illegal migrants without papers.

But it became increasingly difficult for Diego to keep this information from his friends, to explain why the family never went to Mexico, why he could not pass his driving test, why he could not get a job.

It was a struggle. He came into contact with drug dealers but resisted temptation. "It was sometimes really hard to stay on track. I thought that I never would be able to finish college or later go to a university because I didn't have any papers. So why keep studying so hard?"

But he persevered. He did not want to disappoint his mother who had done everything for his and his sister's education. Once he told the truth to a new girlfriend who had come over from Mexico legally. She was shocked. She said she would rather be white. "Well, I just said: thanks for dating."

No papers, no stipend

Diego was so good at school that his teachers recommended him for a college preparation course. He passed and like the others he had to fill out forms to get a stipend. "But I couldn't. I didn't have any status, no social security number. I just thought: And now I am really f*****."

Once again, though, he refused to give up because of his mother, who had had to quit school: "I wanted to be the first in the family with a college degree."

Finally, he spoke to this supervisor, telling her the truth. She too was shocked but sought advice from her colleagues. None had any experience of schoolchildren without papers in this white suburb. "I again felt so much like an outsider," recalls Diego.

In 2012, President Barack Obama announced that his administration would stop deporting young undocumented individuals who matched certain criteria previously proposed under the DREAM Act. Diego was able to get a work permit, pass his driving test and lead a halfway normal life, although his status was not yet entirely legal. He remained cautious at first; worried that Obama would lose the elections, and Matt Romney would become president. Would he be deported after all this time? And his mother and his sister too? "But then something happened in this summer. I just couldn't take it anymore and had my coming out at a press conference."

This was a huge relief. Most of his friends were shocked. Not about his origins, but because he had kept his story secret for so long.

"My coming out gave me such an energy boost, I felt freed on a deep level.“

Plans to emigrate if Trump wins

Diego was able to apply for a stipend. Organizations such as The Dream US Scholarship helped him to pay his college fees. He could work, help support his family finally.

Does he feel American today? "I still have issues with this statement. I don't agree that people have to assimilate. People should be able to keep their culture."

Diego is due to graduate from college in two months. Then he plans to work for two years before realizing his dream to go to university. "I will be the first in my family with a college degree. And I want to be the first with a PhD."

He doesn't doubt his ability to make it. "I am probably smart, and I know how to work hard." But there is a snag. "I am already making plans for what to do if Donald Trump gets elected. I am debating if I should go to Mexico or Canada.“

Wouldn't it be tough to leave the US? "I am here and I am not here. I am only here when they want me to. I still have no rights. Somehow the flight has never ended."